You have some options open to you, which could be
used in combination.
1) Use all 7 wires - one group of 3 in parallel
for 1 side of the supply, and the remaing 4 in
parallel for the other side of the supply. That
will reduce losses in the wire.
2) Reduce the current drawn by the device(s)
at the top of the hill, if possible.
3) Use higher voltage AC as the source and step it
down, rectify and regulate at the top of the hill.
4) Use batteries at the top of the hill and charge
them from the source at the end at the bottom.
#4 is viable only if the load at the top of the hill
draws current intermittently. Even then, you would
need to determine if on time versus off time allows
the battery to recharge at whatever charge rate the
setup would allow.
What about adding a solar panel to option 4? Solar powered fencers
are getting to be fairly common. Even if the panel can't keep up the
battery wouldn't have to be exchanged as often for a fully charged one.
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No. 8 has a diameter of 0.1285 inches. 0.1285 inches is 128.5
thousandths of an inch. CMA is 128.5 squared or 16512 circualr
mils. The distance of 500 meters = 500 x 3.28 feet = 1640 feet Load
= 0.5 amperes
K or circular mil ohms per foot for galvanized soft steel wire is not
easy to find, but 95.8 at 20 degrees C is given by one standard. This
is about 9 times that of copper that is 10.371 for 20 degrees C.
This is a voltge drop of 9.5/12 x 100 or 79 percent.
To achieve a voltage drop of 5 percent maximum:
0.05 x 12 = 0.6 volts
CMA = 2(95.8)(1640)(0.5)/0.6
CMA=261,853 which is about the size of a 250 Kcmil conductor.
This assumes a low temperature of 20 degrees C. which is 68 degrees F.
Voltage drop at room temperature will be more.
Therefore, No 8 the steel wire cannot be used without having too high
of a voltage drop.
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